Specialized fasteners for surgical (e.g., medical) applications are known in the art. In typical surgical applications, these specialized fasteners (e.g., screws) are fastened to the tissue (e.g., bone tissue) of a patient. Surgical fasteners are often used with other devices, such as pins, braces, and plates, in the setting and immobilization of bone fractures, as well as in other applications. Often, conventional surgical fasteners are fastened to the tissue by forming a hole in the tissue at a placement site and threading the fastener into the hole. This procedure commonly requires a medical professional performing the procedure to position the fastener proximate the placement site with one hand and with the other hand articulating an installation tool to drive the fastener into the hole in the tissue. Handling the fastener separately from the installation tool occupies both of the medical professional's hands and can be burdensome, awkward, and difficult to maintain a grip on and accurately place the fastener. Additionally, directly manually handling the fastener can increase the likelihood of harmful germs and bacteria transferring from the medical professional to the fastener prior to insertion into the tissue, and increase the likelihood of damage to the fastener.
Commonly, surgical fasteners are temporary, and require removal after surgery or at any of various times throughout a healing process. Orthopedic fasteners can require removal at some time following surgery for various reasons. For example, a fastener embedded in bone can act as a stress riser, which may increase the risk of an undesired fracture in the bone proximate the fastener location. Additionally, over time, the position of a fastener can shift away from the initial embedded position, which may result in an infection or other negative side effect. At the very least, an un-removed fastener may simply cause discomfort, such as by conducting cold temperatures, or creating pain and irritation in the tissue surrounding the fastener. Although less likely, an un-removed fastener may result in the potential inconvenience associated with metal detector false alarms. In addition to potentially negative consequences caused by leaving hardware fixed in a patient's bone, some negative effects may be caused during the installation of the hardware. For example, a fastener may become damaged during the process of insertion, such as stripping the head or breaking the head off entirely. Such damage to the head can make further insertion and/or extraction of the fastener highly problematic.
The nature of bone itself also presents some challenges to removing a temporary fastener. As the bone heals, it tends to encase the fastener more tightly, which can increase the torque required to loosen the fastener from the bone. The bone may also encroach upon the head of the fastener making it difficult to access. Another problem arises from the hollow nature of bones. When removing a screw, once the threaded portion has been unscrewed from the distal cortex of the bone, there may be insufficient resistance offered by the screw head to keep the installation tool engaged. Moreover, even if the screw can be extracted to the point where the proximal end of the threaded portion comes into contact with the proximal cortex of the bone, the bone may have grown tightly around the shank, which can impede further progress. Accordingly, when removing a fastener, there may be insufficient resistance to keep the installation tool engaged in the head for the threads to bite.
Some conventional fasteners employ various head and installation tool receptacle designs in an attempt to improve the coupling between the fastener and installation tool, which can improve the process of installing and removing fastener. However, such conventional fasteners often fail to provide adequate coupling between the fastener and installation tool for both installation and removal of a fastener, particularly where one-handed operation in medical and surgical applications is desired. Some systems include installation tools that secure the fastener to the installation tool prior to installation and removal in an attempt to facilitate one-handed operation. These systems, however, fail to provide adequate ease in operation and robustness necessary for many medical applications, as well as suffer from other significant shortcomings.
Additionally some conventional fasteners (e.g., bone implants) are designed for permanent placement, as opposed to temporary placement. Many of these permanent fasteners and the associated installation tools are not equipped to remove the fasteners following implantation, especially when a high-torque is necessary for removal. Moreover, these permanent fasteners and installation tools are often deficient for installing fasteners in applications requiring a high-torque for installation.
One particular conventional permanent implant described in U.S. Patent Application Publication No. 2008/0249577, filed Apr. 2, 2008, (“the '577 Publication”) includes a dome-shaped (i.e., hollow hemispherical shaped) head. The hemispherical surface of the head is designed to match the contour of a load-bearing surface of a joint. The dome-shaped head has small notches about an outer periphery of the head which can be engaged by an installation tool specifically designed for use with the implant having the dome-shaped head. The installation tool includes several arms that can be actuated to engage the small notches during installation and disengage the notches when installation is complete. Because the outer surface of the implant will act as a load-bearing surface when installed, the outer surface is designed to be substantially smooth and free of irregularities. Accordingly, the notches are sized and shaped to occupy a significantly small portion of the outer surface (e.g., the outer surface area is maximized while the notch size is minimized). The arms are likewise small and flexible for engaging and disengaging the notches. Because the notches and arms are small, the permanent implant and installation tool are not sufficiently robust to handle many high-torque medical applications. Additionally, the arms are angled to enter the notches in an outer-to-inner direction such that a significant portion of the arms protrude outwardly from the outer periphery of the dome-shaped head (see FIG. 4(b) of the '577 Publication). The outwardly protruding arms would be prone to catching or disturbing tissue adjacent the implant during installation of the implant.
Other challenges analogous to those discussed above may also exist in non-medical fastener applications, such as applications involving materials (e.g., wood, metal, and plastic), or any applications where a reliable, easily operable, and secure fastener, and/or system and method for insertion and/or removal of the fastener is desired.